1. Field of the Invention
The present invention relates to a method for serving a handoff in a mobile communication system and, more particularly, to a method for serving a packet dormant handoff in a mobile communication system.
2. Background of the Related Art
FIG. 1 illustrates a configuration of a mobile communication system that serves a packet data communication according to a related art and the present invention. The mobile communication system includes a mobile station (MS) 101; a base transceiver station (BTS) 102 connected with the mobile station 101 by a radio link; a base station controller/packet control function (BSC/PCF) 103 connected with the base transceiver station (BTS) 102; a mobile switching center/visitor location register (MSC/VLR) 104 connected with the BSC/PCF 103; and a home location register (HLR) 105 connected with MSC/VLR 104 to communicate with other communication networks 106, such as a PSTN, PCS, and public land mobile network PLMN.BSC/PCF 103 is connected to an intranet 108 through PDSN 107 and then connected to Internet 109.
In the mobile communication system constructed as above, if the mobile station 101 requires CDMA 2000 packet data service, BSC/PCF 103 decides a destination of the PDSN 107 for transmitting the packet data. At this time, the radio traffic channel and radio link protocol are established in the radio interval between the mobile station 101 and the base station controller. Also, an A8 traffic link for transferring point-to-point protocol (PPP) link data between the mobile station 101 and the PDSN 107 is established between the base station controller and the packet control function. An A10 radio-packet link for transferring the PPP link data between the mobile station 101 and the PDSN 107 is established between the packet control function and the PDSN 107. Here, the A8 interface carries user traffic between the base transceiver station and the packet control function, while the A10 interface carries the user traffic between the packet control function and the PDSN 107.
At this time, the connection of the packet data service at the mobile station 101 is achieved as an active state or an inactive state for the packet data service. The packet data service inactive state represents a state in which the mobile station 101 is not served by the packet data service. The mobile station 101 can convert the packet data inactive state to the packet data active state when a packet data service activation, such as a call origination for the packet data by the mobile station's user or an activation according to another manner, is performed. The packet data service active state establishes and maintains the PPP link between the mobile station 101 and the PDSN 107 and between the packet control function and the PDSN 107, as described above.
The packet data service active state is operated with a packet active state or a packet dormant state according to the radio link state. Here, the packet active state maintains the A8 link by occupying the radio traffic channel at the mobile station 101. Additionally, the packet active state maintains the radio link protocol (RLP) and facilitates the communication of packet data. The packet dormant state controls the mobile station 101, at the base station controller, by releasing the radio channel, the A8 link, and the radio traffic channel.
FIG. 2 is a time sequential chart illustrating control procedures (step a1 to step n1) of serving a packet dormant handoff of a related art. First, an origination message is transmitted (step a1) from a mobile station to a target BSC/PCF, in a state in which a data ready to send (DRS) signal is set as “0.” The origination message gets the packet data service when a new packet zone identifier arrives. The target BSC/PCF transmits an acknowledge response message to the mobile station (step b1) upon receiving the origination message. The target BSC/PCF prepares a connection management (CM) service requirement message and transmits it to a mobile switching center (step c1). Also, a timer T303 is driven at the same time in step c1.
Next, the mobile switching center sends a request for the assignment of radio resources to the target BSC/PCF, in response to the service requirement message, and a timer T10 is driven (step d1). The target BSC/PCF stops the timer T303 upon receiving the assignment request.
The target BSC/PCF sends a request for A11 registration to a target PDSN (step e1) to support the packet data service. The registration request message includes a mobility event indicator, within the vendor/organization specific extension. At this time, the target BSC/PCF drives a timer, Tregreq, representing a timer registration requirement.
Next, the target PDSN transmits an All registration reply message to the target BSC/PCF (step f1). At this time, the target BSC/PCF stops the timer Tregreq. The A11 interface carries signaling information between the PCF and the PDSN.
The traffic channel and PPP link are established between the target BSC/PCF and the mobile station as result of each above step, thereby registering a mobile IP (MIP) in step g1. And the base station transmits an assignment complete message to the mobile station in step h1. At this time, the mobile switching center stops the timer T10.
At some point, the All registration life timer for the A10 link, in the source PDSN, shall expire. Then, the source PDSN transmits an All registration renewal message to the source BSC/PCF, as the notification of the re-registration and the source PDSN drives a timer, Tregupd (step i1). Next, the source BSC/PCF transmits an A11 registration recognition message to the source PDSN (step j1) and the source PDSN stops the timer, Tregupd.
Since the mobile station 101 handoffs from the source to the target, the source BSC/PCF requires the A11 registration, with lifetime 0, as the notification of the A10 link release, without renewal to the source PDSN to record the related information (step k1). The source PDSN transmits the A11 registration response message, with lifetime 0, to the source BSC/PCF in response to the registration request (step l1). At this time, the source PDSN stores the related information recorded for additional processes before transmitting the A11 registration response message. And the source BSC/PCF terminates the A10 connection for the mobile station and stops the timer Trefreq.
Periodically, when the registration lifetime of the BSC/PCF A11/A10 link registration is expired, the BSC/PCF shall renew the registration by the registration request message. So, the target BSC/PCF transmits the A11 registration request message to the target PDSN to record the related information (step m1). Then, the target PDSN transmits the A11 registration response message to the target BSC/PCF (step n1).
The above steps from i1 to l1 are not aligned with steps m1 and n1, which occur when the lifetime is expired. Steps m1 and n1 are irrelevant to steps i1˜l1.
Referring to FIGS. 1 and 2, the mobile switching center does not transfer the information of the dormant handoff to the source BSC/PCF, when the mobile station is moved during the dormant state from an area of the source or old BSC/PCF into an area of the target or new BSC/PCF, in the related art. Hereinafter, the cause will be explained in detail with reference to FIG. 2.
The operation will be explained under the conditions that the mobile station is moved from an area “A” of the first BSC/PCF into an area “C” of the second BSC/PCF.
Packet data serving node 1 (PDSN1) “B” is not a prospective packet data serving node for a handoff connection, when the mobile station has already established a current PPP link with it. But the packet data serving node 2 (PDSN2) “D” is a prospective target when the mobile station is moved from an old area of the first BSC/PCF into a new area of the second BSC/PCF. In this case, the mobile switching center provides the information for performing the dormant handoff to a new target BSC2/PCF2, thereby setting the radio-protocol link between the new target BSC2/PCF2 and the new target PDSN2. Also, the new target PDSN2 resets the PPP link and transmits an FA advertisement to register the MIP registration, since the MIP mobile station is newly visited.
However, it is noted that the mobile switching center does not transfer the dormant handoff information to the source BSC1/PCF1 and the source packet data serving node. Accordingly, the old source PDSN1 can release the radio-protocol link only when it registers an A10 MIP time out, an upper layer PPP link time out, or the MIP registration time out, as shown in step i1 of FIG. 2. Hence, there is a drawback that the radio-protocol link resource of the old source PCF and IP resource of the old source PDSN are wasted until the time out is completed.